1. Field of the Invention
The present invention relates to a document illumination apparatus, a document reading apparatus and an image forming apparatus, and more particularly to one or more of these apparatuses permitting efficient cooling of a lamp.
2. Discussion of the Related Art
It is known to use an illumination apparatus in a document reading apparatus of an image forming system, such as a copiers or a scanner. The illumination apparatus uses a fluorescent lamp as a light source to illuminate a document, so that the document can be read by the reading apparatus.
The fluorescent lamp is commonly a xenon lamp which has a high emission efficiency and relatively low power consumption. The xenon lamp has a wider light emitting area and generates a greater amount of light, although it has a lower brightness as compared to a halogen lamp.
The amount of light emitted by the lamp is proportional to an area of the glass tube coated with a fluorescent material. Thus, a relatively large xenon lamp, such as a xenon lamp having a size of 10 mm or more in diameter, is used to emit a large amount of light.
The known illumination apparatus suffer from the disadvantage that the large xenon lamp produces a relatively large amount of heat. High temperatures within the illumination apparatus adversely affect the longevity of the light source, and degrade other components of the illumination apparatus.
Further, the adverse effects caused by these high temperatures are compounded as illumination apparatuses are continually reduced in size. In order to make the illumination apparatuses more compact, it has been proposed to use more reflectors to provide the light path. However, the use of more reflectors increases the complexity of the illumination apparatuses, and it is more difficult and expensive to provide an accurate light path.